COM method return correct value only when it invoked with pause intervals

Question

I have COM object, which I initialize it at once:

ISTIPositionPtr _position;

CoInitializeEx(NULL, COINIT_APARTMENTTHREADED);
_position.CreateInstance(__uuidof(STIPosition));

Next I have function, that invoke method of this COM object:

LPSAFEARRAY saValues;
structSTIPositionUpdate* pVals;
long count;
float sum = 0;  

if (SUCCEEDED(_position->GetPositionList(&saValues, &count))) {
    if (SUCCEEDED(SafeArrayAccessData(saValues, (void**)&pVals))) {
        for (int i = 0; i < count; ++i) {
            sum += pVals[i].fDollarsBot;
        }
        SafeArrayUnaccessData(saValues);
    }
    SafeArrayDestroy(saValues);
}

return sum;

Problem is that the method:

 _position->GetPositionList(&saValues, &count)

Return correct value or zero. but if I invoke function with pause intervals, then all works fine. I don't know, probably this is asynchronous method and I must use some mechanisms, that wait until method will be finished?

For example:

long count = 0;
while (count == 0) {
    _position->GetPositionList(&saValues, &count)
}

Answer 1

I found that is need to initialize saValues:

LPSAFEARRAY saValues = NULL;

and then all works as expected.